Evaluation of activated carbon synthesized by one-stage and two-stage co-pyrolysis from sludge and coconut shell

Alien species water hyacinth realizes waste into treasure: The preparation of biomass sorbent to determine benzoylurea insecticides in tea products

A fast and effective analytical method with biomass solid-phase microextraction sorbent combined with a high-performance liquid chromatography-ultraviolet detector was proposed for the determination of benzoylurea (BU) insecticides in tea products. The novel sorbent was prepared by activating and then carbonizing water hyacinth with a fast growth rate and low application value as raw material and showed a high specific surface area and multiple interactions with analytes, such as electrostatic action, hydrogen bonding, and π-π conjugation. After optimizing the three most important extraction parameters (pH [X1], sample loading rate [X2], and solution volume [X3]) by Box-Behnken design, the as-established analytical method showed good extraction performance: excellent recovery (80.13%-106.66%) and wide linear range (1-400 µg/L) with a determination coefficient of 0.9992-0.9999, a low limit of detection of 0.02-0.1 µg/L and the satisfactory practical application results in tea products. All these indicate that the water hyacinth-derived material has the potential as a solid-phase extraction sorbent for the detection and removal of BU insecticides from tea products, and at the same time, it can also achieve the effect of rational use of biological resources, maintaining ecological balance, turning waste into treasure, and achieving industrial production.

Preparation of a highly functionalized activated carbon from waste third-monomer pressure filter liquid for removal of methylene blue in aqueous solution

Third monomer dimethyl isophthalate-5-sodium sulfonate (SIPM) is an additive widely used to modify polyester chips. During the manufacture of SIPM, large amounts of waste third-monomer pressure filter liquid are produced. As the liquid contains lots of toxic organics and highly concentrated Na₂SO₄, it will cause serious environmental pollution if discharged directly. In this study, highly functionalized activated carbon (AC) was prepared by directly carbonizing the dried waste liquid under ambient pressure. Structural and adsorption properties of the prepared AC were analyzed and evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), N₂ adsorption-desorption analysis and methylene blue (MB) as the adsorbate, respectively. Results showed that the adsorption capacity of the prepared AC to MB reached the highest when carbonization was conducted at 400 °C. XRD analysis showed that the AC has a disordered graphite-like crystal structure. FT-IR and XPS analyses showed that there were plenty of carboxyl and sulfonic functional groups in the AC. The adsorption follows the pseudo-second-order kinetic model and the isotherm process is consistent with the Langmuir model. The adsorption capacity increased with increasing solution pH and dropped when the solution pH exceeded 12. Increasing solution temperature favors the adsorption, where the maximum value can reach as high as 2816.4 mg g^-1 at 45 °C, more than double the values reported to date. The adsorption of MB on the AC is mainly controlled by the electrostatic interaction between MB and the anionic form of carboxyl and sulfonic groups.

Development of sludge-based activated char sorbent with enhanced hydrophobicity for oil spill cleanup

Recovery of oil spilled on surface waters by the use of sorbents remains one of the primary oil spill response options available. To improve on this response measure, we have successfully fabricated an activated char (AC) sorbent material by pyrolysis of sewage sludge (SS), a readily available waste product generated across the world from wastewater treatment plants. The inherent Fe-minerals in SS texture were converted to magnetic Fe₃O₄ particles during the pyrolysis reaction. The AC provided a unique means to recover the sorbent after the oil sorption process with a magnetic field. Meanwhile, a superhydrophobic sorbent material with a water contact angle of 152.2° was created by the treatment of AC with myristic acid which could float on the water surface. Feasibility studies at the laboratory-scale were conducted with motor oil and light crude oil to evaluate its potential use in spill response operations. Results showed a sorption capacity of about 8.5 and 10.7 g/g for motor oil and light crude oil, respectively. Following the recovery of the test oils by ethanol stripping, the material could be recycled up to 5 times with trivial loss in sorption capacity. This research proposes a framework for the development of a highly efficient sorbent material for oil spill response operations from SS waste.

Aerobic granular sludge cultivated from Fe-loaded activated carbon as carrier working low-strength wastewater conditions by bioreactor

This study proposes a new method to promote the granulation process while accelerating the degradation efficiency of nutrients. The new strategy could involve preparing Fe-loaded activated carbon (FAC) before start-up of granular cultivation and then cultivating the process of aerobic granular sludge (AGS) with such materials. In addition, this experiment could further comprehend how the preparation and characteristics of FAC affect the formation and properties of AGS. The conclusions showed that compared with the control, FAC enhanced the sedimentation performance and significant removal efficiency. Meanwhile, the values of protein (PN) and polysaccharide (PS) also increased significantly in the addition of FAC, indicating the production of substances were induced by FAC. Molecular biology methods indicated that the rapid production of granulation and removal of nutrients were considered as the abundance of various microbes and denitrifying bacteria at the addition of FAC. This research showed that the presence of FAC is a useful strategy for the initiation of sludge particle formation to promote the treatment of wastewater, containing COD and NH₄⁺ at about 150-100 and 30 mg L^-1.

A review of prospects and current scenarios of biomass co-pyrolysis for water treatment

With ever-growing population comes an increase in waste and wastewater generated. There is ongoing research to not only reduce the waste but also to increase its value commercially. One method is pyrolysis, a process that converts wastes, at temperatures usually above 300 °C in a pyrolysis unit, to carbon-rich biochars among with other useful products. These chars are known to be beneficial as they can be used for water treatment applications; certain studies also reveal improvements in the biochar quality especially on the surface area and pore volume by imparting thermal and chemical activation methods, which eventually improves the uptake of pollutants during the removal of inorganic and organic contaminants in water. Research based on single waste valorisation into biochar applications for water treatment has been extended and applied to the pyrolysis of two or more feedstocks, termed co-pyrolysis, and its implementation for water treatment. The co-pyrolysis research mainly covers activation, applications, predictive calculations, and modelling studies, including isotherm, kinetic, and thermodynamic adsorption analyses. This paper focuses on the copyrolysis biochar production studies for activated adsorbents, adsorption mechanisms, pollutant removal capacities, regeneration, and real water treatment studies to understand the implementation of these co-pyrolyzed chars in water treatment applications. Finally, some prospects to identify the future progress and opportunities in this area of research are also described. This review provides a way to manage solid waste in a sustainable manner, while developing materials that can be utilized for water treatment, providing a double target approach to pollution management.

Sustainable Downstream Separation of Itaconic Acid Using Carbon-Based Adsorbents

Separation of itaconic acid from aqueous solution has been explored using various carbon-based adsorbents obtained from the pyrolysis and KOH activation of coconut shell biomass. The best preparation conditions to obtain a tailored adsorbent for itaconic acid purification were identified via a Taguchi experimental design, where its adsorption properties were maximized. The best activated carbon was obtained via coconut shell pyrolysis at 750 °C for 4 h plus an activation with 0.1 KOH and a final treatment at 800 °C for 2 h. This adsorbent showed an adsorption capacity of 4.31 mmol/g at 20 °C and pH 3 with a surface area of 466 m2/g. Itaconic acid separation was exothermic and pH-dependent where electrostatic forces and hydrogen bonding were the main adsorption interactions. Calculated adsorption rate constants for itaconic acid adsorption were 0.44–1.20 h-1. Results of adsorbent characterization analysis indicated the presence of a crystallization of itaconic acid molecules onto the activated carbon surface where 3–4 molecules could interact to form the clusters. This organic acid was recovered from the adsorbent surface via desorption with water or ethanol, thus facilitating its final purification. The best activated carbon obtained in this study is a promising alternative to perform sustainable and energy-efficient downstream separation and purification of itaconic acid produced via fermentation.

Multi-step preparation of Fe and Si modified biochar derived from waterworks sludge towards methylene blue adsorption

A magnetic nitrogen-doped sludge-based biochar (NAlSB-Fe-Si) was prepared based on waterworks sludge for raw material and dicyandiamide for nitrogen source to adsorb methylene blue (MB) from water. And the magnetic particles loaded on the adsorbent were obtained through functionalizing iron and silicon ions which were extracted from the biochar by acid and alkali impregnation. Physicochemical properties of sludge-based biochar (SB) were analyzed by SEM, BET, FTIR, XRD, XPS and VSM. Compared with the original biochar, NAlSB-Fe-Si had richer pore structure and higher pore volume, and the SiO₂ and Fe₃O₄ loading made the specific surface area increased by 200%. Possible adsorption mechanism was proposed by exploring the initial pH, MB concentration and reaction time. Results revealed that alkaline environment was more conducive to the rapid removal of cationic dyes such as MB. Pseudo-second-order kinetic model and intra-particle diffusion model could describe the adsorption behavior of MB on NAlSB-Fe-Si. The fitting results of Langmuir model showed that adsorption temperature is positively correlated with adsorption capacity, and the maximum adsorption capacity of MB on nitrogen-doped sludge-based biochar (NSB) and NAlSB-Fe-Si at 25 °C was 26.47 and 300.36 mg/g, respectively. Finally, the MB removal rate of NAlSB-Fe-Si could still reach 70% after four cycles, indicating that the composite was an efficient cationic dye adsorbent, and its preparation could be regarded as a way of resource utilization of waterworks sludge.

Synthesis and performance evaluation of adsorbents derived from sewage sludge blended with waste coal for nitrate and methyl red removal

Low-cost adsorbents were synthesized using two types of sewage sludge: D, which was obtained during the dissolved air flotation stage, and S, which was a mixture of primary and secondary sludge from the digestion and dewatering stages. The sewage sludge was mixed with waste coal before being activated with potassium hydroxide (KOH) and oxidized with ammonium persulfate (APS). The nitrate and methyl red removal capacities of the synthesized adsorbents were evaluated and compared to those of industrial activated charcoal. The oxidation surface area of adsorbents derived from sludge S shrank by six fold after modification i.e., from 281.72 (unoxidized) to 46.573 m2/g for the oxidized adsorbent with a solution of 2M ammonium peroxydisulfate, while those derived from D only varied narrowly from 312.72 to 282.22 m2/g, but surface modification had no effect on inorganic composition in either case. The adsorption of nitrate and methyl red (MR) was performed in batch mode, and the removal processes followed the pseudo second order kinetic model and the Langmuir isotherm fairly well. The adsorption capacities of nitrate and MR were higher at pH = 2 and pH = 4, respectively.

Adsorption of Sulfonamides in Aqueous Solution on Reusable Coconut-Shell Biochar Modified by Alkaline Activation and Magnetization

Biochar is a low-cost adsorbent for sorptive removal of antibiotics from wastewater, but the adsorption efficiency needs to be improved. In this study, coconut-shell biochar was activated with KOH to improve the adsorption efficiency and magnetically modified with FeCl₃ to enable recycling. The amount of KOH and the concentration of FeCl₃ were optimized to reduce the pollution and production cost. The KOH-activated and FeCl₃-magnetized biochar gave good sulfonamide antibiotic (SA) removal. The maximum adsorption capacities for sulfadiazine, sulfamethazine and sulfamethoxazole were 294.12, 400.00 and 454.55 mg g⁻¹, respectively, i.e., five to seven times higher than those achieved with raw biochar. More than 80% of the adsorption capacity was retained after three consecutive adsorption-desorption cycles. A combination of scanning electron microscopy, Brunauer-Emmett-Teller analysis, X-ray diffraction, Fourier-transform infrared and Raman spectroscopies, and magnetic hysteresis analysis showed that KOH activation increased the specific surface area, porosity, and number of oxygen-rich functional groups. Iron oxide particles, which were formed by FeCl₃ magnetization, covered the biochar surface. The SAs were adsorbed on the modified biochar via hydrogen bonds between SA molecules and -OH/-COOH groups in the biochar. Investigation of the adsorption kinetics and isotherms showed that the adsorption process follows a pseudo-second-order kinetic model and a monolayer adsorption mechanism. The adsorption capacity at low pH was relatively high because of a combination of π⁺-π electron-donor-acceptor, charge-assisted hydrogen-bonding, electrostatic, and Lewis acid-base interactions, pore filling, van der Waals forces and hydrophobic interactions. The results of this study show that magnetically modified biochar has potential applications as an effective, recyclable adsorbent for antibiotic removal during wastewater treatment.

Pretreatment, modification and applications of sewage sludge-derived biochar for resource recovery- A review

With the quick increase in industrialization and urbanization, a mass of sludge has been produced on the account of increased wastewater treatment facilities. Sewage sludge (SS) management has become one of the most crucial environmental problems because of the existence of various pollutants. However, SS is a carbon-rich material, which has favored novel technologies for biochar production, which can be utilized for dissimilar applications. This review systematically analyzes and summarizes the pretreatment, modification, and especially application of sewage sludge-derived biochar (SSBC), based on published literature. The comparative assessment of pretreatment technology such as pyrolysis, hydrothermal carbonization, combustion, deashing, and co-feeding is presented to appraise their appropriateness for SS resource availability and the production of SSBC. In addition, the authors summarize and analyze the current modification methods and divide them into two categories: physical properties and surface chemical modifications. The applications of SSBC as absorbent, catalyst and catalyst support, electrode materials, gas storage, soil amendment, and sold biofuel are reviewed in detail. Furthermore, the discussion about the existing problems and the direction of future efforts are presented at the end of each section to envisage SS as a promising opportunity for resources rather than a nuisance.

Preparation of a Novel Activated Carbon from Cassava Sludge for the High-Efficiency Adsorption of Hexavalent Chromium in Potable Water: Adsorption Performance and Mechanism Insight

Particularly, because of the leakage risk of metal elements from sludge carbon, little attention has been focused on using sludge activated carbon as an adsorbent for the removal of Cr (VI) from contaminated water sources. Herein, a novel sludge carbon derived from dewatered cassava sludge was synthesized by pyrolysis using ZnCl2 as an activator at the optimal conditions. The prepared sludge activated carbon possessed a large BET surface (509.03 m2/g), demonstrating an efficient removal for Cr (VI). Although the time to reach equilibrium was extended by increasing the initial Cr (VI) concentration, the adsorption process was completed within 3 h. The kinetics of adsorption agreed with the Elovich model. The whole adsorption rate was controlled by both film and intra-particle diffusion. The Cr (VI) removal efficiency increased with elevating temperature, and the adsorption equilibrium process followed the Freundlich isotherm model. The adsorption occurred spontaneously with endothermic nature. The removal mechanism of Cr (VI) on the prepared sludge activated carbon depended highly on solution pH, involving pore filling, electrostatic attraction, reduction, and ion exchange. The trace leakage of metal elements after use was confirmed. Therefore, the prepared sludge activated carbon was considered to be a highly potential adsorbent for Cr (VI) removal from contaminated raw water.

Microwave-assisted pyrolysis of oily sludge from offshore oilfield for recovery of high-quality products

Microwave pyrolysis of oily sludge (OS) was investigated in this study. In this case, the highest oil yield (85.93 wt%) was achieved at 500 °C. The molar ratio of H/C was lower for OS char (OC) at higher pyrolysis temperatures, indicating good stability of OC owing to high degree of carbonization and aromaticity. Then, iodine adsorption value of OC reached maximum (531.2 mg/g) at 750 °C. While methylene blue (MB) uptake slightly increased with temperature and reached maximum (384.08 mg/g) at 850 °C. In order to improve the quality of pyrolysis products, different catalysts were employed in OS pyrolysis. The maximum content (64.31%) of aromatic hydrocarbon was found in PO500-10β. In addition, β-zeolite also reduced oxygenates content in oil, beneficial for stability of oil products. The gas products from catalytic pyrolysis were abundant in CO and CH₄, and KOH achieved the highest CO (5.9 wt%), CH₄ (16.9 wt%) and H₂ (2.4 wt%) yields. Finally, a reaction mechanism pathway for OS pyrolysis was proposed to show the production routes of gas, liquid, and solid products.

Toxicity and remediation of pharmaceuticals and pesticides using metal oxides and carbon nanomaterials

The worldwide development of agriculture and industry has resulted in contamination of water bodies by pharmaceuticals, pesticides and other xenobiotics. Even at trace levels of few micrograms per liter in waters, these contaminants induce public health and environmental issues, thus calling for efficient removal methods such as adsorption. Recent adsorption techniques for wastewater treatment involve metal oxide compounds, e.g. Fe2O3, ZnO, Al2O3 and ZnO-MgO, and carbon-based materials such as graphene oxide, activated carbon, carbon nanotubes, and carbon/graphene quantum dots. Here, the small size of metal oxides and the presence various functional groups has allowed higher adsorption efficiencies. Moreover, carbon-based adsorbents exhibit unique properties such as high surface area, high porosity, easy functionalization, low price, and high surface reactivity. Here we review the cytotoxic effects of pharmaceutical drugs and pesticides in terms of human risk and ecotoxicology. We also present remediation techniques involving adsorption on metal oxides and carbon-based materials.

The evaluation of immobilization behavior and potential ecological risk of heavy metals in bio-char with different alkaline activation

The bio-char was prepared by co-pyrolysis of municipal sewage sludge and biomass with chemical activation. The alkaline activating agents of KOH and K₂CO₃ were used to develop multilevel pore structure without heavy metal. The proximate analysis, ultimate analysis, SEM, and surface area and porosity analyzer were applied to present the physico-chemical properties and multilevel pore structure of bio-char. After impregnation pretreatment, the KOH provided more functional ingredients and reacted with C to expand pore structure for bio-chars. It was confirmed the specific surface area reached 2122.43 m²/g, and micropore area was 1674.85 m²/g after co-pyrolysis at 800 °C. Through the pretreatment of alkaline activation, the novel evaluation of heavy metal immobilization behavior in bio-char matrix were investigated by BCR sequential extraction and leaching tests. The KOH activation showed prominent immobilization behavior relatively, and the K₂CO₃ activation had more noticeable effects on leaching behavior. For Cu, Ni, Cr, Cd, Pb, and Zn, after co-pyrolysis at 900 °C, the proportion of unstable fraction decreased significantly, and the residual fractions of heavy metals were above 89.44% according to BCR sequential extraction procedure. Under optimal pyrolysis temperature, the E_r value of bio-char reduced to 41.93, and the potential ecological risks decreased from considerable risk to low risk to ensure the further eco-friendly application.

Preparation of composite sludge carbon-based materials by LDHs conditioning and carbonization and its application in the simultaneous removal of dissolved organic matter and phosphate in sewage

In this work, a novel carbon-based hydrotalcite-like compounds materials (LDO-SBCs) were prepared by coupling layered double hydroxides (LDHs) conditioning and pyrolytic carbonization, and characterized by X-ray diffraction (XRD), Thermogravimetric Analyzer (TGA), X-ray photoelectron spectroscopy (XPS) and Brunner-Emmet-Teller (BET) measurements. The synthesized LDO-SBCs composites were used in wastewater treatment for simultaneous removal of phosphate and dissolved organic matter (DOM). The adsorption of DOM and phosphate were well conformed to pseudo-second-order mode. Adsorption equilibrium was better fitted by Langmuir model for phosphate, while Freundlich model for DOM. Compared with the raw sludge carbon, the removal efficiency of DOM and phosphate by LDO-SBCs were increased by 8% and 13%, respectively. Based on the fluorescence spectrum and parallel factor analysis (PARAFAC), LDO-SBCs performed well in promoting the removal of protein substances (TPN and APN). Pore filling, hydrogen bonding, electrostatic adsorption and surface complexation might be dominant in the adsorption of DOM, while, surface complexation and ion exchange between the LDO layers were mainly responsible for the adsorption of phosphate. The difference of adsorption capacity of LDO-SBCs was related to the superior channel structure of composite materials and the composition of interlayer anions of LDO.

An overview on engineering the surface area and porosity of biochar

Surface area and porosity are important physical properties of biochar, playing a crucial role in many biochar applications, such as wastewater treatment and soil remediation. The production of engineered biochar with highly porous structure and large surface area has received extensive attention. This paper comprehensively reviewed the effects of biomass and pyrolysis parameters on the surface area and porosity of biochar. The composition of biomass feedstock and pyrolysis temperature are the major influencing factors. It is suggested that the lignocellulosic biomass is an outstanding candidate, wood and woody biomass in particular. Besides, moderate temperatures (400-700 °C) are suitable for the development of the pore structure. Further improvement can be implemented by additional treatments. Activation is the most widely used and effective way to promote biochar surface area and porosity, especially the chemical activation. Enhancement can also be achieved by using other treatment methods, such as carbonaceous materials coating, ball milling, and templating. Future research should focus on upgrading or developing treatment technology to achieve enhanced functionality and porous structure of biochar simultaneously.

A novel activation-hydrochar via hydrothermal carbonization and KOH activation of sewage sludge and coconut shell for biomass wastes: Preparation, characterization and adsorption properties

A two-stage method of hydrothermal carbonization and chemical activation technology was applied to prepare a novel, large surface area and rich-pore structure activation-hydrochar from sludge sewage and coconut shell due to its mild, low-cost, and well-developed merits. The pore-making mechanism of activation-hydrochar was discussed by FT-IR, XPS, SEM, TG, TG-MS, XRD, and BET characterization. These results illustrated that the first stage of hydrothermal carbonization achieved the rich-pore structure hydrochar via dehydration, decarboxylation, deamination, and rearrangement reactions. The subsequent KOH activation was conducive to the pore-forming process. Specifically, the pore structure of activation-hydrochar was ameliorated and abundant active adsorption sites were obtained by the modification. The adsorption properties of activation-hydrochar on Methylene Blue (MB) and Congo Red (CR) were systematically investigated, and the max adsorption capacities of those were obtained with 623.37 mg/g and 228.25 mg/g, respectively. The pseudo-second-order kinetics and Langmuir models were both fit to elucidate the adsorption process for both dyes. Thermodynamics revealed adsorption performance accompanied by the spontaneous and endothermic processes. In general, the research clearly indicated the synthesis route for activation-hydrochar, and its further adsorption performance, capacity, and mechanism on MB and CR. This research demonstrated that activation-hydrochar with the abundant surface area and rich-pore structure made it a candidate for the production of effective adsorption material. It is prospective to achieve the utilization of wastes and its further application in wastewater treatment.

Combination of biochar and immobilized bacteria accelerates polyacrylamide biodegradation in soil by both bio-augmentation and bio-stimulation strategies

Polyacrylamide (PAM) has been used extensively due to its well-known stable chemical properties, but limited information is available on the biodegradation of soil-containing PAM. In this work, sufficient degradation of PAM was achieved via the addition of the Klebsiella sp. PCX-biochar composite to PAM-containing soil, due to the synergic effect of bio-augmentation and bio-stimulation. The optimal degradation rate of 69.1% over 30-day period was observed under the following conditions: the addition of immobilized bacteria at 0.07 g/g, pH 6.6, and temperature at 38.0 °C. In this study, we showed that PAM was successfully hydrolyzed by amidase, and ammonia in the hydrolysis product was then oxidized by the nitrifying bacteria. The decrease of water-extractable organic carbon (WEOC) also demonstrated the chain cleavage in PAM. PAM was utilized as a carbon source not only by Klebsiella sp. PCX but also by some taxa from indigenous bacteria. Last but not least, it was shown in this study that biochar, even though immobilized with exogenous microorganisms, actually enhanced bacterial diversity and stimulated the growth of some indigenous PAM-degrading taxa. Based on the above observations, we concluded that PAM biodegradation via the addition of bacteria-immobilized biochar was a synergy of both bio-augmentation and bio-stimulation strategies.

Preparation of carbon/Al2O3/nZVI magnetic nanophase materials produced from drinking water sludge for the removal of As(V) from aqueous solutions

Drinking water sludge (DWS) contains organic carbon and metal ions with the potential to prepare adsorbents. In this research, DWS was separated into two parts by acid leaching, i.e., an acid leaching carbonization sludge (ALCS) and an acid leaching solution. Iron and aluminum were extracted from the acid leaching solution and loaded onto ALCS by sedimentation and liquid-phase reduction to prepare a carbon/Al₂O₃/nZVI magnetic adsorption material (ALCS-Al-Fe). The optimum arsenic removal conditions, adsorption kinetics, and isotherm were determined, and the characteristics of the adsorbent ALCS-Al-Fe were investigated. The results showed that the composite exerted a favorable arsenic removal effect due to the electrostatic adsorption of nanometer zero-valent iron as well as ion exchange and complexation between the OH^- groups on the surface of ALCS-Al-Fe and As(V). The pH change had a slight effect on the adsorption capacity, while the common anions SO₄^2- and SiO₃^2- showed obvious inhibitory effects. Considering that alkalinity is beneficial to arsenic ion desorption, NaOH was used in desorbing to conduct 6 cycles of regeneration experiments, and the final removal rate could still reach 90.5%. Therefore, the concept of green development of preparing magnetic adsorbents by using whole component of DWS is significant to the exploitation of sludge recycling.

Effect of dispersant on the synthesis of cotton textile waste-based activated carbon by FeCl2 activation: characterization and adsorption properties

Considering the accumulation and high consumption of activating agents, anhydrous ethanol (AE) could be used to dissolve them to improve the dispersion effect, which was an effective way of improving the practical utilization rate. In this study, FeCl₂ was dissolved in AE and further impregnated cotton textile waste (CTW) to prepare activated carbons (ACs) by pyrolysis. Afterward, ACs prepared in optimal conditions determined by the orthogonal experiment evaluated the physicochemical properties and adsorption capacities for Cr(VI). The results illustrated that AE greatly increased the dispersion of FeCl₂ on CTW, reduced the conventional impregnation dosage, and remarkably improved the activation efficiency. Textural analyses revealed that ACs exhibited excellent porosity properties and graphite carbon structure. FeCl₂ catalyzed the decomposition of volatile substances to produce gaseous products and promoted the transformation of amorphous carbon to graphite carbon that was conducive to pore development, followed by the formation of developed micropores and crystal structures. The adsorption performance of ACs was estimated using Cr(VI), and the adsorption was fitted with the pseudo-second-order kinetic and the Langmuir isotherm. Furthermore, the ACs possessed superior magnetization and reusability. Graphical abstract.

High-Yield Production of Lignin-Derived Functional Carbon Nanosheet for Dye Adsorption

In this article, we report the preparation of lignin-derived carbon nanosheet (L-CNS) by direct thermal treatment of lignin without activation operation and the functions of the L-CNS as an adsorbent for rhodamine dye. The L-CNSs are fabricated by freeze-drying (FD) methods of lignin followed by high-temperature carbonization. It is found that lower frozen temperature in FD or lower concentration of lignin aqueous solution renders L-CNSs' more porous morphology and higher specific surface area (SSA), allowing a promising application of the L-CNSs as an efficient adsorbent for organic pollutants. In particular, the alkaline hydroxide catalyst helps to increase the SSA of carbon products, leading to a further improved adsorption capacity. On the other hand, p-toluenesulfonic acid (TsOH) catalyzed pyrolysis, which dramatically increased the L-CNS product yield, and provided a high-yield approach for the production of pollutant absorbent.

Relationship between the physicochemical properties of sludge-based carbons and the adsorption capacity of dissolved organic matter in advanced wastewater treatment: Effects of chemical conditioning

Pyrolysis carbonisation is a promising technology to convert organic waste into valuable carbon-based materials. However, sludge is generally highly compressible and difficult to dewater because of its high concentrations of biopolymers; the bound water of sludge is trapped in a network composed of biopolymers. Therefore, chemical conditioning is an indispensable step for improving sludge dewaterability performance. In the present work, the effects of different chemical conditioning agents (polymeric aluminium chloride (PACl), iron(III) chloride (FeCl₃), KMnO₄-Fe(II) and Fenton's reagent) on the physicochemical properties of sludge-based carbons (SBCs) were systematically studied and the SBCs were further used in advanced wastewater treatment. The adsorption mechanisms of dissolved organic matters (DOMs) by different SBCs were also investigated. The results showed that conditioning with KMnO₄-Fe(II) and Fenton's reagent improved the specific surface area of the SBCs, whereas inorganic salt flocculation conditioning reduced the porosity of the SBCs. In addition, we found that the Fenton-SBC and Mn/Fe-SBC performed better than the other investigated SBCs in the removal of organic compounds from secondary effluent and that the pseudo-second-order kinetic model could better describe the process of DOMs adsorption by all of the investigated SBCs. Moreover, three-dimensional fluorescence excitation-emission matrix spectroscopy in combination with an analysis of the physical and chemical fractionation of DOMs showed that all of the SBCs performed well in the adsorption of aromatic substances, hydrophobic acids and hydrophobic neutrals, whereas the Mn/Fe-SBC and Fenton-SBC performed better than the other SBCs in the removal of weakly hydrophobic acids.

Three-dimensional hierarchical porous carbon structure derived from pinecone as a potential catalyst support in catalytic remediation of antibiotics

In this study, pinecone was converted via two stage pyrolysis to produce low cost activated carbon. Furnace pyrolysis was used in the first step to convert pinecone to carbonized material, followed by microwave pyrolysis of the carbonized material activated with KOH to obtain activated carbon (ACK) materials as a suitable catalyst support. The ACK samples were characterized by their morphology, structural, adsorption and electrochemical properties. The optimized ACK 2.24-16 prepared from the pinecone had a complex three-dimensional (3D)-hierarchical porous structure, with an abundance of micropores and mesopores compared to other ACK samples judging from the high iodine number (1900 mg g^-1) and the methylene blue number (4000 mg g^-1) capacity. The optimized ACK 2.24-16 had the highest current response and least charge transfer resistance, along with moderate surface area (427 m² g^-1) as a promising photocatalyst support. The 3D hierarchical porous ACK significantly assisted catalyst dispersion, and enhanced visible light absorption and fast interfacial charge transfer. This work shows the promising aspect of utilizing pinecone to produce a low-cost photocatalyst support for environmental remediation.

Adsorption of dissolved organic matter from landfill leachate using activated carbon prepared from sewage sludge and cabbage by ZnCl2

Sewage sludge and cabbage (Brassica oleracea) were used to prepare activated carbon by high-temperature inert carbonization with the activator ZnCl₂. The physicochemical characteristics of the sludge-based activated carbon (SAC) were analyzed, and the effects on the removal of chemical oxygen demand (COD) from the landfill leachate by the adsorbent dosage, adsorption time, and the solution pH were investigated in different adsorbents. Three-dimensional fluorescence spectroscopy and gas chromatography-mass spectrometry were used to analyze the organic compounds in the leachate before and after adsorption. The results demonstrated that the average iodine content of the SAC was 535.01 mg/g. The average specific surface area was 917.72 m²/g, and the dominant pore size was in the mesoporous range. The optimum parameters for adsorption were a dosage of 3%, adsorption time of 60 min, and pH = 8, and the COD removal rate reached 85.61%. The adsorption of COD on the SAC was best fitted by the Freundlich model. Additionally, the SAC was found to have a high removal efficiency for refractory organic matter and short-chain alkanes, such as humic acid-like substances, in the leachate but was not effective for long-chain alkanes.